1. Field of the Invention
The present invention relates to an elastic member which is used in image formation equipment such as electrophotographic equipment, electrostatic recording equipment and toner flying recording equipment. More particularly, the present invention is concerned with an elastic member which has low surface-friction-resistance and fine cells; and with image formation equipment equipped with the aforesaid elastic member.
Moreover, the present invention relates to a toner supply roller in a developing apparatus of a printer for electrophotography, electrostatic recording and the like. More particularly, the present invention pertains to a toner supply roller mounted on a developing apparatus which comprises a toner cartridge accommodating a toner as a developer, the toner supply roller and a developing roller, and which forms toner image by supplying the toner to a static latent image on the surface of a photosensitive body.
2. Description of the Related Arts
In recent years, accompanying the advancement of electrophotographic technique, an intermediate-resistance elastic roller has attracted attention as a transfer member, a toner supply member, an electrifying member and the like each for dry electrophotographic equipment, and is used as a transfer roller, a developing roller, a toner supply roller, an electrifying roller and the like. Incidentally, there have heretofore been employed a high molecular elastomer and high molecular foam each having rubbery elasticity as a material constituting the above-mentioned intermediate-resistance elastic roller.
Examples of the members which have hitherto been employed for the above-mentioned purpose include such elastomer or foam as NBR, EPDM, silicone rubber, polyurethane and the like, which is imparted with electroconductivity with electroconductive carbon such as carbon black, a metal oxide, an ionic electroconductive agent or the like. There are also employed, depending upon the purpose of use, non-electroconductive members that are not incorporated with an electroconductivity imparting agent.
Of the elastomer or foam as mentioned above, polyurethane is preferably used in the aforesaid electroconductive member, since polyurethane can be made into a low hardness member well suited for the above-mentioned member, and can be made into a low hardness foam by a method using such a foaming agent as water and a compound having a low boiling point, a mechanically agitational method or the like method. Further, it is possible to lower the hardness of polyurethane foam by selecting a raw material which determines the chemical structure of polyurethane and its blending amount.
There is used a roller which comprises urethane foam or silicone foam as a toner supply member in electrophotographic equipment. The urethane foam is widely used because of its high mechanical strength and inexpensiveness in comparison with silicone foam.
In electrophotographic equipment, a toner is supplied from a toner cartridge onto a developing roller through a toner supply roller. In this case, the toner is repeatedly subjected to compression or friction between the toner supply roller and the developing roller, sometimes bringing about agglomeration or fused adhesion. As a result, there is caused as the case may be, defective images wherein streaky unevenness in color appears in an electrophotograph by the accumulation of agglomerates or fusedly adhered matters between the developing roller and a developing blade. In order to prevent such defective images, it is deemed necessary to lower the friction resistance on the surface of a toner supply roller.
Among a variety of methods available for lowering the friction resistance on the surface of a toner supply roller, it is considered to be effective to employ silicone which exerts such effect that enhances the lubricity and improve slidability.
There are available various methods for applying silicone to a toner supply roller composed of polyurethane foam. It has been confirmed by the present inventors that the friction resistance on the surface of a toner supply roller can greatly be lowered by coating the surface thereof with silicone by means of spraying or the like, for which patent application has been made by the present inventors. Incidentally, the above-mentioned method enables to lower the surface friction resistance and assure favorable images in the early stage but, when a printing endurance test is effected for a long period of time, sometimes brings about defective images due to agglomeration or fused adhesion of a toner depending upon the printing conditions.
In addition, a method in which silicone as a blending agent for urethane is added to a starting material for urethane foam, fails in many cases to assure objective foam having fine and uniform cells, since the addition of silicone inhibits the stability of cells at the time of urethane foaming because of the anti-foaming properties or foam breaking properties inherent in silicone. In the case of a toner supply roller, since it is required in particular that the cells be fine (50 to 200 numbers/25 mm) and uniform, how to stabilize the cells has been a technological subject of much importance in the case of adding silicone.
In recent years, there has widely been introduced an electroconductive roller system in a developing roller and toner supply roller that are employed in a developing apparatus which is arranged on a developing process in electrophotographic equipment such as an electronic copying machine, laser beam printer and facsimile machine. In the foregoing system, the toner supply roller is rubbed against the developing roller so as to frictionally electrify the toner, and thus is required to possess a stable friction property (pressing force) with the developing roller and also an enhanced toner supply property to frictional portions and positions.
Such being the case, in conventional toner supply rollers of this type, there is generally employed a foamed elastic material wherein rubber or polyurethane has been foamed.
However, as a result of investigation made by the present inventors on the performance of the conventional toner supply roller comprising the foamed elastic body, it has been proved that when the toner which is conveyed to a developing roller is fusedly adhered to a toner regulating blade and the fusedly adhered toner layer gradually grows to such an extent that it interferes with the toner layer supported on the developing roller, then there is formed a portion through which the toner layer supported thereon can not pass, and development is made in the absence of the toner in the aforesaid limited portion with a result that there are often caused such troubles as unprinted white portion in the developed image owing to failure to supply the toner.
It is an object of the invention to provide an elastic member which has low surface-friction-resistance and fine cells, and which comprises silicone-modified polyurethane foam; and also image formation equipment equipped with the above-mentioned elastic member.
It is another object of the invention to provide a developing apparatus which is capable of assuring images free from any trouble such as unprinted white portion due to failure to supply a toner, and which comprises a toner supply roller mounted thereon and composed of a foamed elastic body.
Other objects of the invention will be obvious from the text of this specification hereinafter disclosed.
In such circumstances, intensive extensive research and investigation were accumulated by the present inventors on an elastic member which has low surface-friction-resistance and fine cells, and which comprises silicone-modified polyurethane foam. As a result, it has been found that silicone-modified polyurethane foam is obtainable which has fine uniform cells, surface friction resistance of at most 1.0 N and the number of cells in the range of 50 to 200/25 mm, by using a modified silicone oil bearing a functional group reactive with isocyanate as a modified silicone oil and a foam stabiizer which comprises a polyether-modified silicone containing 50 to 100% by weight of a polyoxyethylene unit in the polyether moiety; and that an elastic member comprising such polyurethane foam is well suited as a member mounted on image formation equipment.
Moreover, as a result of investigation made by the present inventors on a toner supply roller which has brought about the above-mentioned defective image, the following has been found. Specifically, while simultaneously with toner supply a toner supply roller rubs a toner against a developing roller for the purpose of electrifying the toner existing between the toner supply roller and the developing roller, when the rubbing force is too strong, an increase in damage to the toner deteriorates itself, whereby the toner thus deteriorated is liable to be adhesively solidified.
Further accumulated investigation led to the findings that the above-mentioned rubbing force is greatly influenced by the hardness and the friction resistance of the toner supply roller and also by the pressing force between the toner supply roller and the developing roller; and that trouble-free images can be formed, when the hardness (compression spring constant) and the friction resistance of the toner supply roller as well as the pressing force between the toner supply roller and developing roller are each set on an appropriate value.
Thus the present invention has been accomplished on the basis of the foregoing findings and information.
That is to say, the present invention provides an elastic member which comprises (A) polyurethane foam obtained by agitationally mixing a urethane prepolymer, a foaming agent and a foam stabiizer, wherein the urethane prepolymer is synthesized from a polyol and a polyisocyanate in the presence of a modified silicone oil added thereto, or (B) polyurethane foam obtained by agitationally mixing a polyol, a polyisocyanate, a modified silicone oil, a foaming agent and a foam stabiizer, wherein the modified silicone oil is a modified silicone oil bearing a functional group reactive with a polyisocyanate and the foam stabiizer is a foam stabiizer which comprises a polyether modified silicone containing 50 to 100% by weight of a polyoxyethylene unit in the polyether moiety; and also provides image formation equipment equipped with the aforesaid elastic member.
In addition thereto, the present invention provides a toner supply roller constituted of a foamed elastic member mounted on a developing apparatus which comprises a toner cartridge that accommodates a toner as a developer, the toner supply roller and a developing roller, and which forms a toner image by supplying the toner to a static latent image on the surface of a photosensitive body, characterized in that the toner supply roller has a compression spring constant in the range of 0.25 to 5.0 N/mm and a surface friction resistance in the range of 0.4 to 1.2 N.